Portable battery packs are commonly used to power various forms of electrical devices which may be used in explosive types of environments, as found in mines, chemical treatment plants and flour mills to name only a few. For example, portable battery packs are used to power lamps which are commonly affixed to the worker's helmet. Should the cable supplying power to the lamp be cut or abraded so as to short or cause an overcurrent condition, sparks can be generated which could set off an explosion in the environment.
An approach to preventing short circuits damaging circuitry for lamp power pack is disclosed in U.S. Pat. No. 4,317,162. A fusable link is used in the circuitry to prevent a short damaging the circuitry. However no consideration is given to reacting immediately to a short to limit current flow and prevent sparks which could set off an explosion.
The electronic circuitry, according to this invention for a battery pack, overcomes this problem to provide a system which is classified as intrinsically safe for use in mines and other similar explosive environments.